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diff --git a/absl/random/internal/fast_uniform_bits_test.cc b/absl/random/internal/fast_uniform_bits_test.cc
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index 000000000000..f4b9cd5fcc6d
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+++ b/absl/random/internal/fast_uniform_bits_test.cc
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+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/random/internal/fast_uniform_bits.h"
+
+#include <random>
+
+#include "gtest/gtest.h"
+
+namespace {
+
+template <typename IntType>
+class FastUniformBitsTypedTest : public ::testing::Test {};
+
+using IntTypes = ::testing::Types<uint8_t, uint16_t, uint32_t, uint64_t>;
+
+TYPED_TEST_SUITE(FastUniformBitsTypedTest, IntTypes);
+
+TYPED_TEST(FastUniformBitsTypedTest, BasicTest) {
+  using Limits = std::numeric_limits<TypeParam>;
+  using FastBits = absl::random_internal::FastUniformBits<TypeParam>;
+
+  EXPECT_EQ(0, FastBits::min());
+  EXPECT_EQ(Limits::max(), FastBits::max());
+
+  constexpr int kIters = 10000;
+  std::random_device rd;
+  std::mt19937 gen(rd());
+  FastBits fast;
+  for (int i = 0; i < kIters; i++) {
+    const auto v = fast(gen);
+    EXPECT_LE(v, FastBits::max());
+    EXPECT_GE(v, FastBits::min());
+  }
+}
+
+TEST(FastUniformBitsTest, TypeBoundaries32) {
+  // Tests that FastUniformBits can adapt to 32-bit boundaries.
+  absl::random_internal::FastUniformBits<uint32_t, 1> a;
+  absl::random_internal::FastUniformBits<uint32_t, 31> b;
+  absl::random_internal::FastUniformBits<uint32_t, 32> c;
+
+  {
+    std::mt19937 gen;  // 32-bit
+    a(gen);
+    b(gen);
+    c(gen);
+  }
+
+  {
+    std::mt19937_64 gen;  // 64-bit
+    a(gen);
+    b(gen);
+    c(gen);
+  }
+}
+
+TEST(FastUniformBitsTest, TypeBoundaries64) {
+  // Tests that FastUniformBits can adapt to 64-bit boundaries.
+  absl::random_internal::FastUniformBits<uint64_t, 1> a;
+  absl::random_internal::FastUniformBits<uint64_t, 31> b;
+  absl::random_internal::FastUniformBits<uint64_t, 32> c;
+  absl::random_internal::FastUniformBits<uint64_t, 33> d;
+  absl::random_internal::FastUniformBits<uint64_t, 63> e;
+  absl::random_internal::FastUniformBits<uint64_t, 64> f;
+
+  {
+    std::mt19937 gen;  // 32-bit
+    a(gen);
+    b(gen);
+    c(gen);
+    d(gen);
+    e(gen);
+    f(gen);
+  }
+
+  {
+    std::mt19937_64 gen;  // 64-bit
+    a(gen);
+    b(gen);
+    c(gen);
+    d(gen);
+    e(gen);
+    f(gen);
+  }
+}
+
+class UrngOddbits {
+ public:
+  using result_type = uint8_t;
+  static constexpr result_type min() { return 1; }
+  static constexpr result_type max() { return 0xfe; }
+  result_type operator()() { return 2; }
+};
+
+class Urng4bits {
+ public:
+  using result_type = uint8_t;
+  static constexpr result_type min() { return 1; }
+  static constexpr result_type max() { return 0xf + 1; }
+  result_type operator()() { return 2; }
+};
+
+class Urng32bits {
+ public:
+  using result_type = uint32_t;
+  static constexpr result_type min() { return 0; }
+  static constexpr result_type max() { return 0xffffffff; }
+  result_type operator()() { return 1; }
+};
+
+// Compile-time test to validate the helper classes used by FastUniformBits
+TEST(FastUniformBitsTest, FastUniformBitsDetails) {
+  using absl::random_internal::FastUniformBitsLoopingConstants;
+  using absl::random_internal::FastUniformBitsURBGConstants;
+
+  // 4-bit URBG
+  {
+    using constants = FastUniformBitsURBGConstants<Urng4bits>;
+    static_assert(constants::kPowerOfTwo == true,
+                  "constants::kPowerOfTwo == false");
+    static_assert(constants::kRange == 16, "constants::kRange == false");
+    static_assert(constants::kRangeBits == 4, "constants::kRangeBits == false");
+    static_assert(constants::kRangeMask == 0x0f,
+                  "constants::kRangeMask == false");
+  }
+  {
+    using looping = FastUniformBitsLoopingConstants<uint32_t, 31, Urng4bits>;
+    // To get 31 bits from a 4-bit generator, issue 8 calls and extract 4 bits
+    // per call on all except the first.
+    static_assert(looping::kN0 == 1, "looping::kN0");
+    static_assert(looping::kW0 == 3, "looping::kW0");
+    static_assert(looping::kM0 == 0x7, "looping::kM0");
+    // (The second set of calls, kN1, will not do anything.)
+    static_assert(looping::kN1 == 8, "looping::kN1");
+    static_assert(looping::kW1 == 4, "looping::kW1");
+    static_assert(looping::kM1 == 0xf, "looping::kM1");
+  }
+
+  // ~7-bit URBG
+  {
+    using constants = FastUniformBitsURBGConstants<UrngOddbits>;
+    static_assert(constants::kPowerOfTwo == false,
+                  "constants::kPowerOfTwo == false");
+    static_assert(constants::kRange == 0xfe, "constants::kRange == 0xfe");
+    static_assert(constants::kRangeBits == 7, "constants::kRangeBits == 7");
+    static_assert(constants::kRangeMask == 0x7f,
+                  "constants::kRangeMask == 0x7f");
+  }
+  {
+    using looping = FastUniformBitsLoopingConstants<uint64_t, 60, UrngOddbits>;
+    // To get 60 bits from a 7-bit generator, issue 10 calls and extract 6 bits
+    // per call, discarding the excess entropy.
+    static_assert(looping::kN0 == 10, "looping::kN0");
+    static_assert(looping::kW0 == 6, "looping::kW0");
+    static_assert(looping::kM0 == 0x3f, "looping::kM0");
+    // (The second set of calls, kN1, will not do anything.)
+    static_assert(looping::kN1 == 10, "looping::kN1");
+    static_assert(looping::kW1 == 7, "looping::kW1");
+    static_assert(looping::kM1 == 0x7f, "looping::kM1");
+  }
+  {
+    using looping = FastUniformBitsLoopingConstants<uint64_t, 63, UrngOddbits>;
+    // To get 63 bits from a 7-bit generator, issue 10 calls--the same as we
+    // would issue for 60 bits--however this time we use two groups.  The first
+    // group (kN0) will issue 7 calls, extracting 6 bits per call.
+    static_assert(looping::kN0 == 7, "looping::kN0");
+    static_assert(looping::kW0 == 6, "looping::kW0");
+    static_assert(looping::kM0 == 0x3f, "looping::kM0");
+    // The second group (kN1) will issue 3 calls, extracting 7 bits per call.
+    static_assert(looping::kN1 == 10, "looping::kN1");
+    static_assert(looping::kW1 == 7, "looping::kW1");
+    static_assert(looping::kM1 == 0x7f, "looping::kM1");
+  }
+}
+
+TEST(FastUniformBitsTest, Urng4_VariousOutputs) {
+  // Tests that how values are composed; the single-bit deltas should be spread
+  // across each invocation.
+  Urng4bits urng4;
+  Urng32bits urng32;
+
+  // 8-bit types
+  {
+    absl::random_internal::FastUniformBits<uint8_t, 1> fast1;
+    EXPECT_EQ(0x1, fast1(urng4));
+    EXPECT_EQ(0x1, fast1(urng32));
+  }
+  {
+    absl::random_internal::FastUniformBits<uint8_t, 2> fast2;
+    EXPECT_EQ(0x1, fast2(urng4));
+    EXPECT_EQ(0x1, fast2(urng32));
+  }
+
+  {
+    absl::random_internal::FastUniformBits<uint8_t, 4> fast4;
+    EXPECT_EQ(0x1, fast4(urng4));
+    EXPECT_EQ(0x1, fast4(urng32));
+  }
+  {
+    absl::random_internal::FastUniformBits<uint8_t, 6> fast6;
+    EXPECT_EQ(0x9, fast6(urng4));  // b001001 (2x3)
+    EXPECT_EQ(0x1, fast6(urng32));
+  }
+  {
+    absl::random_internal::FastUniformBits<uint8_t, 6> fast7;
+    EXPECT_EQ(0x9, fast7(urng4));  // b00001001 (1x4 + 1x3)
+    EXPECT_EQ(0x1, fast7(urng32));
+  }
+
+  {
+    absl::random_internal::FastUniformBits<uint8_t> fast8;
+    EXPECT_EQ(0x11, fast8(urng4));
+    EXPECT_EQ(0x1, fast8(urng32));
+  }
+
+  // 16-bit types
+  {
+    absl::random_internal::FastUniformBits<uint16_t, 10> fast10;
+    EXPECT_EQ(0x91, fast10(urng4));  // b 0010010001 (2x3 + 1x4)
+    EXPECT_EQ(0x1, fast10(urng32));
+  }
+  {
+    absl::random_internal::FastUniformBits<uint16_t, 11> fast11;
+    EXPECT_EQ(0x111, fast11(urng4));
+    EXPECT_EQ(0x1, fast11(urng32));
+  }
+  {
+    absl::random_internal::FastUniformBits<uint16_t, 12> fast12;
+    EXPECT_EQ(0x111, fast12(urng4));
+    EXPECT_EQ(0x1, fast12(urng32));
+  }
+
+  {
+    absl::random_internal::FastUniformBits<uint16_t> fast16;
+    EXPECT_EQ(0x1111, fast16(urng4));
+    EXPECT_EQ(0x1, fast16(urng32));
+  }
+
+  // 32-bit types
+  {
+    absl::random_internal::FastUniformBits<uint32_t, 21> fast21;
+    EXPECT_EQ(0x49111, fast21(urng4));  // b 001001001 000100010001 (3x3 + 3x4)
+    EXPECT_EQ(0x1, fast21(urng32));
+  }
+  {
+    absl::random_internal::FastUniformBits<uint32_t, 24> fast24;
+    EXPECT_EQ(0x111111, fast24(urng4));
+    EXPECT_EQ(0x1, fast24(urng32));
+  }
+
+  {
+    absl::random_internal::FastUniformBits<uint32_t> fast32;
+    EXPECT_EQ(0x11111111, fast32(urng4));
+    EXPECT_EQ(0x1, fast32(urng32));
+  }
+
+  // 64-bit types
+  {
+    absl::random_internal::FastUniformBits<uint64_t, 5> fast5;
+    EXPECT_EQ(0x9, fast5(urng4));
+    EXPECT_EQ(0x1, fast5(urng32));
+  }
+
+  {
+    absl::random_internal::FastUniformBits<uint64_t, 48> fast48;
+    EXPECT_EQ(0x111111111111, fast48(urng4));
+    // computes in 2 steps, should be 24 << 24
+    EXPECT_EQ(0x000001000001, fast48(urng32));
+  }
+
+  {
+    absl::random_internal::FastUniformBits<uint64_t> fast64;
+    EXPECT_EQ(0x1111111111111111, fast64(urng4));
+    EXPECT_EQ(0x0000000100000001, fast64(urng32));
+  }
+}
+
+}  // namespace